The invention relates to a device and a method for detecting the impact of an object on a vehicle. The device comprises a hose filled with a filling medium, which hose has a first end and a second end situated opposite the first end. A first pressure sensor is connected with the first end of the hose, and a second pressure sensor is connected with the second end of the hose, where the first and the second pressure sensor each providing a signal representing the pressure of the filling medium. The device further has an electronic control unit which is connected by way of connection lines with the first and the second sensor for the exchange of data, the electronic control unit being designed for the processing of the signals received by the first and the second pressure sensor.
Such a device is installed particularly in pedestrian protection systems in the front bumper of a vehicle. The device consists of two electric pressure sensors which are tightly connected with one another by means of a highly flexible hose, for example, made of rubber, caoutchouc or Latex. The hose is normally filled with air, in which case the pressure prevailing in the interior of the hose corresponds to the ambient pressure as a result of a pressure compensation element provided in the hose. As a rule, the pressure compensation element consists of a membrane through which the air can penetrate in both directions. However, the membrane is designed such that no water and no dirt can penetrate into the interior of the hose. An adaptation of the pressure prevailing in the interior of the hose to the ambient pressure takes place within seconds, for example, when driving over a mountain pass or in the case of large temperature fluctuations. The pressure sensors are electrically connected by way of connection lines to an electronic control unit (ECU). Usually, but not always, the signal transmission from the pressure sensors to the electronic control unit takes place by way of the connection lines. In the same manner, the pressure sensors are also supplied with the voltage required for their operation by way of the connection lines.
An external force effect on the hose results in a pressure change of the pressure prevailing in the interior of the hose (interior pressure). The pressure change is recorded by the two pressure sensors. Depending on the location at which the pressure admission or external force effect takes place, the sensing of the pressure change at the two pressure sensors can take place in a staggered manner. The analysis of the pressure change takes place in the electronic control unit or, as an alternative, in an analyzing unit connected on the output side of the electronic control unit. In particular, in this case, the time curve of the pressure change is analyzed. As a function of the results of the analysis, a decision takes place concerning the triggering of suitable protective measures. In the case of a pedestrian protection system, the protective measures could consist of lifting the engine hood of the vehicle, so that, after an impact of a person's head and/or body, a longer deformation path is available for the reduction of energy. The protective measures may also comprise a window airbag (pedestrian protection airbag). The person's injuries may thereby be alleviated.
The pressure sensors used in the above-described device may be derivatives of conventional pressure sensors, as used, for example, in the doors of a vehicle for recognizing a side impact. Such sensors are based on detecting a changed pressure. This means that each measurement determines the pressure difference with respect to the last measured value. As a result, a pressure curve is thereby analyzed. Such sensors are diagnosable. This means that it can be determined by the electronic control unit or the analyzing unit connected on the output side whether a respective pressure sensor is operational per se.
The linking of the hose to the pressure sensors usually takes place in that the hose ends are fitted over corresponding connection pieces of the pressure sensors. A mechanical fixing can take place by way of clamps (other fixing methods are also conceivable). Over time, the hose may become brittle or porous, for example, as a result of temperature influences or friction points. Likewise, tears of the hose cannot be excluded. Also, during the operation of the device, even when a new part is installed, it cannot be ensured that the hose and the linkage of the hose to the pressure sensors are tight. However, the operability of the device for detecting the impact of an object can therefore no longer be reliably ensured.
Leakage points have the result that a pressure change of the air in the interior of the hose resulting from an external force effect, e.g., the impact of an object, cannot be recognized or cannot be sufficiently recognized. This has a direct effect on the algorithm used for detecting an impact and therefore on the decision concerning the triggering of a protective measure. In the worst case, such as a torn hose or an opened-up hose linkage at one of the pressure sensors, under certain circumstances a pressure change may even no longer be detectable at any of the two pressure sensors, so that no protective measures are triggered when a pedestrian impacts on the vehicle.
So far, no diagnosis with respect to the operability of the hose has been possible. It is therefore also not possible to determine whether the signals supplied by the two pressure sensors are plausible, because it cannot be ensured in principle that the device as a whole is operable. For this reason, such devices are designed such that the triggering of the protection device can already take place on the basis of a signal transmitted by one pressure sensor.
It is therefore an object of the present invention to indicate a device and a method for detecting the impact of an object on a vehicle, which permit the diagnosability of the entire device.
These objects are achieved by a device according to the characteristics set forth in the independent claims hereof. Advantageous further developments are indicated in the dependent claims.
The invention provides a device for detecting the impact of an object on the vehicle. The device comprises a hose filled with a filling medium, which hose has a first end and a second end situated opposite the first end. A first pressure sensor is connected with the first end of the hose. A second pressure sensor is connected with the second end of the hose. The first and the second pressure sensor each provide a signal representing the pressure of the filling medium. The device further comprises an electronic control unit which is connected by way of connection lines with the first and the second sensor for the exchange of data, the electronic control unit being designed for the processing of the signals received by the first and the second pressure sensor.
According to the invention, the hose is sealed off with respect to the environment and the first and the second pressure sensor, so that the internal pressure of the filling medium prevailing in the hose is independent of an ambient pressure and thereby dependent on a temperature fluctuation. The electronic control unit is designed for processing temperature-caused changes of the internal pressure during the operation of the vehicle as a criterion for the diagnosis of the operability of the device.
As a result of the fact that the hose is sealed off with respect to the environment and the first and the second pressure sensors, the internal pressure of the hose is uncoupled from the ambient air pressure. Temperature fluctuations, which influence the internal-pressure, occur with each drive of the vehicle. These slow pressure changes are used as a criterion for a diagnosis of the operability of the hose. When, in the reverse case, no pressure change takes place in the driving operation, i.e. a respective drive or a respective driving cycle, it can be concluded that there is a leaky hose or leaky linkage of the hose to at least one of the two pressure sensors. It thereby becomes possible to not only diagnose the pressure sensors with respect to their operability, but it now becomes possible to, for the first time, also check the hose indirectly with respect to its operability during the operation of the motor vehicle.
A sealing-off of the sensors with respect to the environment is achieved in that the sensors comprise no pressure compensation element. Likewise, it is provided that the first and the second pressure sensor comprise no ventilation openings or possibly existing ventilation openings of the pressure sensors are sealed off in an airtight manner. Ventilation openings of the pressure sensors, if present, have the purpose of providing a redundant pressure compensation with respect to a pressure compensation element. This is particularly necessary when the pressure compensation element is arranged in the bumper of the vehicle such that it may become soiled and can therefore no longer carry out its function.
It may further be provided that the diagnosis of the operability of the device comprises a processing of the internal pressure for at least several minutes and/or one driving cycle. A time period of several minutes may be required for generating a temperature-caused pressure fluctuation of the internal pressure. As an alternative or in addition, the diagnosis of the hose can also be carried out permanently in a driving operation between the switching-on and switching-off of the ignition. This driving operation will then represent a driving cycle. Optionally, there is also the possibility of carrying out the monitoring during stationary periods and, for example, evaluate day/night temperature differences.
The electronic control unit is optionally designed for evaluating the pressure curve of the internal pressure for diagnosing the operability of the device. It may be determined that a device is functional when, within a preset time period since the starting point in time, a preset pressure change is determined in the pressure curve. Likewise, a pressure change can be detected by changed air pressure and by a changing of the vehicle height with respect to sea level, i.e. when driving over mountain passes.
The electronic control unit may also be designed for determining, for the diagnosis of the operability of the device, a pressure difference of the internal pressure between a starting point in time and a measuring point in time, an operable device being assumed when the pressure difference exceeds a predefined threshold value for a preset time period and/or a driving cycle. In this case, the exceeding of a few millibars of pressure difference is sufficient as a threshold value in order to draw a conclusion on the operability of the hose and the connections of the hose to the pressure sensors.
The time period described in the first-mentioned embodiment and the time difference between the measuring point in time and the starting point in time may basically be the same. In principle, they may also be selected to differ.
It is further advantageous for the device to be placed in the bumper of the vehicle adjacent to a heat source of the vehicle in order to, during the operation of the vehicle, particularly after a start of the vehicle, within a predefined time period, generate a temperature-caused internal-pressure change of the filling medium in the hose. The placing of the device adjacent to a heat source, for example a heat exchanger or the engine itself, permits a faster diagnosis of the operability of the hose because the temperature rise will be relatively high within a short time. If a spatial arrangement directly adjacent to a heat-radiating component is not possible, it may optionally be provided to cause air, which is heated by the components generating waste heat, to flow onto the device.
It is sufficient for the pressure sensors to have a measuring range of more than ±20 mbar, particularly more than ±50 mbar and most preferably of ±100 mbar. This enlarged measuring range also makes it possible to detect only slight temperature-caused pressure differences. This is necessary, for example, when the temperature-caused pressure changes are caused only as a result of a change of the ambient temperature.
It is further provided that the measuring range is selected as a function of the volume and type of filling medium provided in the hose. The dynamics of the measuring range of the pressure sensors can thereby be taken into account.
In principle, it is conceivable to use the pressure sensors from known pedestrian protection systems in a device according to the invention. The initially described pressure sensors, which detect a changed pressure, can, for example, be used.
The device according to the invention has the advantage that, as a result of the elimination of pressure compensation elements and the use of pressure sensors which comprise no ventilation openings, it can be provided more cost-efficiently than the known devices.
Furthermore, high-expenditure mounting devices can be eliminated when the device is integrated in the bumper. Such mounting devices are normally used for protecting the hose from damage, so that no tears or damages will occur during the operation of the vehicle. This is necessary because up to now no diagnosis of the operability of the hose could be carried out.
As a result of the fact that now, in addition of the pressure sensors, the hose and its linkage to the pressure sensors can be diagnosed, it becomes possible to check the plausibility of the signals supplied by the two pressure sensors with respect to one another. Ensuring the plausibility may, for example, consist of triggering a protection device only when both pressure sensors supply a signal. An increased operational reliability can thereby be provided. As an alternative, an implementation may consist of the fact that a triggering of the protection device already takes place when a signal of a single pressure sensor is present. The signal of the second pressure sensor is supplied to the electronic control unit only for redundancy purposes. The functional reliability of the device can thereby be improved. In particular, this will result in fewer false triggerings.
The invention further provides a method for checking a device for detecting the impact of an object on a vehicle, the device being designed as described above. For diagnosing the operability of the device, in the case of this method, a temperature-caused change of the internal pressure during the operation of the vehicle is processed as a criterion for the diagnosis of the operability of the device.
As an alternative or in addition, pressure changes which result from a height difference during the vehicle operation, can be processed as criteria for the diagnosis of the operability of the device.
The hose and/or its linkage to the first and/or second pressure sensor is determined to be operable when, within a predefined time period and/or a driving cycle since the starting point in time, (i) a predefined pressure change in the pressure curve is determined, (ii) a pressure difference of the internal pressure between a starting point in time and a measuring time point in time exceeds a predefined threshold value, or (iii) when the signals differ that are supplied by the pressure sensors.
The method according to the invention has the same advantages that were described in connection with the device according to the invention.
The invention and its advantages will be described in detail in the following by means of an embodiment in the drawing. The single FIGURE is a schematic view of a device according to the invention for detecting the impact of an object on a vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.